Picassa would be a good (and free) alternative, depending on what you need to do. For general photo organizing, tagging, rating, minor image adjustments and cropping its good enough for me. If you need a RAW converter and more control over image adjustments then its probably not for you.

Personally, I use Picassa to organize my photos (from 5 different cameras) and Lightroom for my RAW converter and when I want more control with adjustments, mainly with images from my D800.